Breastpumps are well known, and generally comprise a hood or shield that fits over the breast, a vacuum pump connected to the hood for generating an intermittent vacuum (or negative pressure) within the breastshield, and a receptacle for expressed milk. Negative pressure is pressure below atmospheric pressure. The intermittent suction action of the vacuum pump serves to pull on the breast and nipple and thereby express milk. The expressed milk typically flows from the hood, through a conduit structure and into a collection container, such as a baby bottle, for storage and later use.
Breastpumps can be manually or electrically operated. With manually operated pumps, the pumping action is done by reciprocating a piston or lever by hand, or compressing a flexible bulb, as shown in Medela's U.S. Publication No. 2004/0039330. With electrically operated pumps, the pumping action generated by a motor driven pump and typically conveyed by an air hose, or air line, that connects to the breastshield assembly.
In most instances, the pressure applied at the breast is a negative pressure (suction). That negative pressure is typically applied to the interior of the breastshield in a singular fashion, that is, without any kind of differential vacuum application over the breastshield as a whole. This has ordinarily been done through a cyclic pattern, e.g., intermittent suction. Breastpumps of this kind, which only pull and release suction, are known as simple pumps.
There are also breastpumps that apply a vacuum pressure and a positive pressure, typically applied to the interior of the breastshield, known as complex pumps. Typically, a vacuum pump that generates a positive pressure, (pressure above atmospheric pressure,) assists in forcing the expressed milk through a valve and into the collection container. A breastpump of the foregoing type is shown in U.S. Pat. No. 4,857,051 to Larsson, the disclosure of which is incorporated herein by reference for further details of a breastpump assembly in general.
Positive pressure opens the valve, often used with breastpumps, to assist in movement of the breast milk through the conduit structure and into the bottle. During pumping, the expelled milk will ultimately be separated from the air drawn back and forth in the air hose, and to and from the breastshield. Some breastpumps use gravity and geometry, such as a splashguard, to separate the milk and air (air being the working fluid), but these breastpumps are often difficult to clean, and the orientation of the breastshield in use may be thereby limited. Other breastpumps use a filter, for example a hydrophobic filter, to prevent milk from entering the air hose and/or pump. That filter can become saturated, shutting down pumping; it must also be cleaned and even periodically replaced. The objective of these efforts is to isolate parts of the breastpump from milk or other liquids/bacteriological material that would constitute a contaminant, or foul the works (such as milk finding its way to the pump mechanism). In institutional settings, for another example, it is desirable to have a pump that can be transferred between mothers, yet the pump mechanism remains isolated from one mother to the next.
Some conventional electric breastpumps also use a moveable, sometimes collapsible, membrane or barrier, that separates the breastshield (including valve) from the pumping mechanism. During operation, two pressures are realized: a first pressure on the vacuum side of the membrane, or pump vacuum, and a second pressure on the breastshield side of the membrane, or breastshield vacuum. The vacuum pump communicates a negative pressure to the membrane via the air hose, such that the first pressure is greater than the second pressure, or in similar terms, the pump vacuum is greater than the breastshield vacuum. This differential vacuum causes the membrane to collapse or move. A problem with some conventional breastpumps of this type is that the membrane may not return to an initial state or position, i.e., it may end up locking or buckling.
This type of breastpump generally requires a positive pressure from the breastshield side of the membrane to push the membrane past a lock or buckle point in order to return the membrane to the non-collapsed state during a breastpump cycle. A breastpump of the foregoing type is shown in U.S. Pat. No. 5,941,847 to Huber. A typical issue with these types of pumps is that leakages, evaporation, expulsion of milk and breast extension hysteresis do not ensure that the membrane returns fully to its initial non-collapsed state without the assistance of a positive pressure.
Some conventional manual breastpumps also include a collapsible or movable membrane that has a significant energy loss in “transferring” vacuum from one side to the other. The mechanical coefficient across the barrier membrane needs dramatic improvement.
Accordingly, a breastpump that reduces or eliminates contamination in the upstream pump air line and pump by isolating the pressure source from the expressed milk is desired to protect the user and prevent damage to the pump mechanism. A much more energy efficient pump system that uses a movable membrane/barrier for vacuum communication is also highly desirable.